1. Description of the Prior Art
The present invention relates generally to instruments used to manipulate orthopedic implants. More particularly, the present invention relates to the manipulation of bone anchoring elements positioned in the spine and longitudinal members interconnecting those elements. While the present invention is particularly useful in spinal surgery, it may find use in other areas of medicine as well.
In many applications, particularly those relating to spinal correction techniques, it is desirable to place a series of implants in a patient's spine prior to inserting a longitudinal member (a rod or a plate) along the spine to interconnect the previously placed implants. On occasion, implants may be vertically spaced from the rod or plate and require a mechanical mechanism to bring the rod or plate into contact with the implant. In the instance of a plate, often the implant is a double threaded bolt with a series of bone screw threads anchoring into the bone and a machine threaded post extending through an opening in the plate. A machine threaded nut slightly larger than the opening in the plate may then be threaded onto the threaded post and tightened to bring the implant closer to the plate. For rod systems, a similar arrangement can be utilized whereby the threaded post of the implant extends through a connector attached to the rod. In these systems a nut is used to draw the implant closer to the connector by progressively threading the nut onto the post of the bone bolt.
Alternatively, it is known to provide a rod introducer mechanism that forces the rod and an implant towards each other. In some cases, the threaded post of a bolt type bone anchor is not long enough to extend through a connector attached to the rod. In this situation a mechanism is used to grasp the bolt and pull it towards the connector until the threaded post extends through an opening in the connector. A threaded nut may then be used to complete the connection to the connector.
In other cases the implant, either a bone screw or spinal hook, includes an open channel to receive the rod. A plug or set screw can be used to close the channel and lock the rod to the implant. In certain surgical techniques a rod is anchored at both ends by at least one implant, resulting in the rod being suspended above a second implant. A mechanism is then required to urge the second implant and rod together to permit connection of the implant to the rod and more particularly to seat the rod within the open channel of the implant. One such instrument marketed by Sofamor Danek Group as part of the Compact CD.TM. system, is an introducer lever C-6903 which resembles a fork with a pair of offset tines. The tines of this device extend over the vertically spaced rod and under either side of an enlarged portion of the implant. Once in place, the fork handle is moved toward the rod thereby forcing the rod and implant together. One problem with this arrangement is that the fork tines must pass between the implant and the bone, which in many cases may be difficult and may result in damage to the bone. Moreover, the connection between the fork tines and the implant is not a secure engagement and may result in the rod introducer slipping during the procedure of forcing the rod into the implant.
Other types of rod introduction devices have overcome the problems associated with the simple fork device by first achieving a secure attachment to the implant with articulated forceps or the like. Various instruments for gripping and handling implants are commonly known. One such instrument has a pair of articulating branches defining a gripping nose opposite a pair of handles. While many varieties of these forceps exist to accomplish various functions during surgery, some are adapted specifically to securely hold an implant, and in particular, a spinal osteosynthesis implant. The gripping nose of one such configuration utilizes a pair of inwardly facing cylindrical projections disposed at the distal end of the gripping nose. The cylindrical projections are adapted to engage corresponding recesses on an implant, thereby providing a secure grip. Because of the small size of many spinal implants and the accompanying difficulty gaining a secure grip with only manual pressure, such forceps are often utilized in the manipulation and placement of the implants.
In addition to providing a nose for gripping implants, many forceps also provide a locking mechanism to hold the forceps in the gripping position once the implant is gripped. A common example is the provision of one half of a ratchet rack on one articulating branch aligned to engage a second half of the ratchet rack on the other articulating branch. Upon movement of the branches towards one another, the separate halves of the ratchet rack come into engagement thereby preventing separation of the articulating branches. As is common with such arrangements, the articulating branches have sufficient flexibility that they may be flexed with respect to one another, thereby disengaging the ratchet racks.
An alternative forcep locking mechanism is disclosed in U.S. Pat. No. 5,423,855 owned by the Sofamor SNC subsidiary of Sofamor Danek Group. This patent shows forceps having an implant gripping nose as previously discussed. In this configuration, the articulating branches are held in the closed position by a spring biased cap disposed on the end of the branches opposite the gripping nose.
In prior systems, once a secure engagement has been accomplished between the forceps and the implant, a separate apparatus is attached between the forceps and the rod. In one such mechanism marketed by Sofamor Danek Group as the TSRH.TM. mini-corkscrew, a threaded rod is threadedly coupled at one end to the forceps and engages the rod at the opposite end. Rotation of the threaded rod urges the rod and implant towards each other. In another mechanism marketed by Sofamor Danek Group as an articulated rod pusher C-6211 for use with the Compact CD.TM. system, forceps grip the implant and a pivoting two piece rod pusher lever is used to urge the rod and implant towards one another. In this device, a lower end of the first member of the rod pusher engages the rod and the upper end of the first member is pivotally attached to the second member of the rod pusher lever. The lower end of a second member engages the forceps while the upper end of the second member is rotated to force the rod and implant towards each other.
U.S. Patent 5,020,519 to Hayes et al. discloses a single mechanism which both grips the rod and has a threaded mechanism to accomplish vertical reduction of the rod into the implant. As this reference discloses, the mechanism must first be attached to the implant and then the rod threaded through the opening between the clamping jaws. This unnecessarily creates a complication for the surgeon, i.e. maintaining both the reduction mechanism and the hook in the desired position while attempting to thread the rod through various implants and the opening in the reduction apparatus. Moreover, once the rod has been reduced into the implant opening, the reduction apparatus interferes with visualizing the implant and rod connection, and with placement of a fastener to hold the rod in the implant.
In addition to the surgical condition where the rod is suspended above the implant, the rod may be laterally offset with respect to the implant. Moreover, in some applications the implant may have an implant opening for receiving the rod which opens to the side, thereby requiring the rod to be laterally introduced into the implant. In these instances, it is often desirable to have mechanical assistance in bringing the rod and implant together to permit securing the rod within the implant. One such device marketed by Synthes Spine as the Universal Spinal System Rod Introduction Pliers is utilized to urge a laterally offset rod into a side opening implant. The Rod Introduction Pliers are used in conjunction with a Hook or Screw Holder device threadedly engaging the implant. One branch of the pliers consists of a barrel while the opposing branch defines a rod engaging surface. In operation, this barrel is placed over the Hook or Screw Hold device and the opposing branch of the pliers engages the offset rod and upon actuation of the plier handles the rod is urged into the implant opening. While this system provides a means to reduce the lateral displacement of the rod, it does not permit the user to additionally reduce any vertical displacement between the rod and the implant. Rather, the barrel of the rod introduction pliers apparently slides freely up and down the hook holder.
In addition to having a need, in some surgical situations, to both laterally approximate the rod to the implant and to vertically reduce the rod into the implant, there is a need to deliver a fastening member to the implant while the rod is securely held in place by the rod reduction apparatus. In some systems, the components required to accomplish reduction are offset with respect to the implant, thereby providing access to the implant to facilitate placement of the fastener once the rod is inserted into the implant. Use of offset instruments to apply force to the rod and implant may impart rotational forces to the implant tending to displace the implant from the desired location. Moreover, in most applications the fastening elements must be relatively small to prevent unnecessary protrusion from the implant. While this is desirable after placement, the small size of the fastener makes handling these items difficult. The difficulty of handling the small fasteners is increased when it is required to place them in the implant that is partially obscured by the rod introduction device. One approach to solving this problem is taken by the Universal Spine System pliers discussed above. In operation, a fastening collar is preloaded over the barrel prior to placement over the hook holder. Once the rod has been inserted into the implant the collar may be advanced over the barrel and engaged with the implant.
One disadvantage to the systems discussed above, is that none of the systems provide both a mechanism for reducing vertical rod offset and lateral rod offset from the bone anchor in a single device. Moreover, many of the systems utilize articulating clamping tips actuated by articulating handles to hold the implants and require a separate apparatus attached to the hook or screw holder to perform manipulation of the rod. It will be appreciated that the various handles extending out of the patient interfere both with vision and work space in an already limited surgical field. Therefore, it is desirable to provide a compact implant holder adapted to perform both vertical and lateral reduction of a rod.
The present invention overcomes the problems associated with the prior art by providing a gripping mechanism and a rod introduction lever for both lateral and vertical approximation in a single convenient instrument.